Automatic telephone system



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Patented Oct. 6, 1936 UNITED STATES PATENT OFFICE'.

AUTOMATIC TELEPHONE SYSTEM Application December 29, 1933, Serial No.704,465

27 Claims. (Ci. 179-27) This invention relates to telephone systems ingeneral, but is concerned more particularly with small systems of thetype commonly known as private automatic exchanges.

Private automatic exchanges are as a rule privately owned by individualsor corporations and are installed in factories or other establishmentsfor providing local service between a small number of local telephonelines and for establishing l connections over trunk lines to the mainofce of the telephone companys network.

The main object of the invention is to provide an improved privateautomatic exchange system of the type shown in Patent No. 1,888,337,issued l Novemr 22, 1932, to John H. Voss, by simplifying and reducingthe cost thereof without sacrilcing any of the desirable operatingfeatures.

The three push-buttons and other auxiliary apparatus mounted in the baseof the telephone 2O shown in the aforesaid patent is eliminated andreplaced in accordance with the present invention by a singlepush-button mounted either in a standard telephone itself or on theaccompanying bell box.

25 Another feature which greatly reduces the cost of this system overthe system shown in the aforesaid patent is that in the old system inits simplest form six conductors were required between the telephonesand the exchange equip- 30 ment while in the present case only twoconductors are required.

Other features of the invention relate to the improved method ofanswering incoming trunk calls, of transferring trunk calls from onesub- 35 scriber to another, and of holding and guarding such trunklines.

Another feature of the invention relates to an improved attendantscabinet which may be cut into service when desired to intercept allincom- 40 ing trunk calls.

Other features of the invention relate mostly to circuit improvementswhich will be apparent from the following detail description of thedrawings comprising Figs. 1 to 7, inclusive, which 45 show by means ofthe usual circuit diagrams a suflicient amount of apparatus to enablethe in vention to be described and understood.

Fig. 1 illustrates in its lower lefthand corner a local subscriberstelephone S equipped with a 50 push-button PB by means of which thesubscriber thereat can make and receive trunk calls, can transfer trunkcalls, and can hold a trunk call while making or receiving local calls.Two line circuits, one for information line #0L and 55 the other forline #03, are shown near the center y of Fig. 1.

The wipers and motor magnet of one of the local finders are shown at theright of Fig. l, together with the multiple connections to the otherlocal and trunk finders and connectors. 5

Fig. 2 shows a group of finder-connector relays for controlling theoperation of one of the finder and connector switch links, the wipers ofwhich are shown in Figs. 1 and 3, respectively.

Fig. 3 shows the connector wipers of this finder i0 connector link, asubscribers line and substation S', and a trunk distributor togetherwith its associated relays.

Fig. 4 at the left shows a finder connector distributor and itsassociated relays and at the right shows a transfer distributor and itsassociated relays.

Fig. 5 at the left shows the equipment at the attendants cabinet and atthe right the wipers and motor magnet of one of the trunk nders togetherwith its multiple connections to the connector and local and trunkfinders.

Figs. 6 and 7 show the relays of one of the two-way trunks, theassociated nder and wipers being shown in Fig. 5. V

Referring now to Fig. 1 in detail, all local subscribers lines, Such asS, are equipped with a standard well-known automatic telephone setcomprising a calling device CD, a receiver R, transmitter T, switchhooksprings SH, ringers RB, and an induction coil. Non-restrictedsubscribers entitled to make and receive trunk calls as well as localcalls have a push-button such as PB mounted in the base of the telephoneor on the associated ringer box. Semi-restricted subscribers entitled toanswer trunk calls but not originate trunk calls are similarly providedwith a push-button, but such subscribers lines are connected to batterythrough a resistance, such as Z, over a conductor, such as 29, to itscorresponding bank contact accessible to iinder wiper |52.

Restricted subscribers are not provided witha push-button and can onlymake and receive local calls. Each subscribers line extends to a linecircuit comprising a two-step line and a cut-olf relay, such as relay|03. The conductors extending from the subscribers line circuitsterminate in the banksof both the local and trunk iinders in theconnector banks.

The finder switches are mechanically similar to the well-known rotarylineswitch having no normal position, while the circuits thereof havebeen altered in accordance with the present invention.

mechanically similar to the finders, but instead of automaticallyhunting for a marked potential as the finder does, the connector isdirectlvely controlled from normal position by impulses.

The trunk distributor shown in Fig. 4 is mechanically similar to thefinders and automatically hunts for an idle trunk line or a. particulartrunk line in use dependent upon whether end to cause such armature tovibrate when the relay releases the armature. Relay 410 in the transferdistributor has a spring 41| with a weight 412 which causes spring 41|to vibrate for a predetermined period when the relay 410 is firstenergized.

Referring now to the attendants equipment shown in Fig. 5, theattendants telephone circuit is mounted on a base and comprises acalling device CD, a handset HS comprising a transmitter and receiver,monophone springs MS which are closed when the handset HS is removedfrom the cradle, an induction coil IC, and ringers RB. 'Ihe informationkey, the hold key, the transfer key, the turn signal key SK, the tworelease and trunk answering keys, (only one of which is shown), and twosupervisory lamps, such as SL, are mounted on top of the base alongsideof the attendants telephone. The relays 5|6 and 500 to 540, inclusive,and the buzzer B are mounted inside the base. In case a second trunkanswer key is provided then another set of relays, such as relays 500 to540 are also provided since such relays are individual to a trunk answerkey. The buzzer B is used when the `attendant answers all incoming trunkcalls while the trunk signals are used when any non-restricted localline may answer incoming trunk calls. There are as many common trunksignals placed throughout the establishment as required to enable thelocal subscribers to determine when an incoming trunk call is to beanswered.

In Figs. 6 and 7, one of a number oi two-way trunk circuits is shownconnecting the local private exchange with one of the telephone companysexchanges which may be either manual or automatic. When the trunkcircuit, shown in Fig. 7 extends to an automatic exchange, a dottedstrap shorting the winding of relay 120 is provided. while this strap iscut when the trunk circuit extends to a manual exchange.

Having described the equipment and apparatus, a detailed description ofthe operation will now be given. Briefly, local calls are completed inthe following manner: The local calling party removes his receiver and,after hearing dial tone, dials the number of the desired station. If thecalled line is not busy, the called f station will be rung automaticallyand inter- The connector switch shown in Fig. 3 is subscriber S' shownin Fig. 4. Responsive to the removal of the receiver, switchhook springSH closes a circuit for energizing the combined line and cut-offtwo-step relay |03 in its rst step as follows: from ground by way ofarmature |08, conductor |02, lower winding of the induction coil,transmitter T, through the impulse springs of the calling 4deviceCDthrough the upper switchhook springs to conductor and thence by way ofarmature |04 through the upper resistance winding and through the lowerwinding of two-step relay |03 to battery. Due to the resistance in theupper winding of relay |03, this relay is energized in its rst step toclose only armatures and |01. At armature |05 relay |03 marks the line Sas calling in the bank of the local finder by connecting. the batterythrough the lower winding of relay |03 to the fifteenth bank contactaccessible to finder wiper |53.

At armature |01, relay |03 grounds the finder start conductor 9 tocomplete a circuit for the start relay 420 in the finder connectordistributor shown in Fig. 4 as follows: from ground by way of armature|06 in its normal position, armature |01 in operated position, commonfinder start conductor 9, through the winding of slowto-operate startrelay 420, armature 422, interrupter springs 404 and through the windingof the distributor motor magnet 405 to battery. Motor magnet 405 ismarginal and will not energize in series with the winding of relay 420or in series with resistance 423. At armature 422 relay 420 removes theobvious short circuit from around resistance 423 for a purpose to bemore fully described hereinafter, and at armature 42| completes anobvious circuit for energizing relay 400. At armature 40| relay 400prepares a point in the circuit for the finder test circuit; at armature402 and its working contact completes the circuit for energizingslow-to-release relay 4|0; and at armature 403 completes the circuit forenergizing the finder motor magnet |68 as follows: from ground by way ofarmature 205, armature 23| and resting contact, conductor 2| 5, bankcontact and Wiper 4|6, armature 403, wiper 4|5 and engaged bank contact,conductor |61, and through the winding of motor magnet |68 to battery.

Magnet |68, upon energizing, positions its pawl preparatory to steppingthe wipers of the local finder and at springs |69 completes the circuitfor energizing the combined line, stepping and test relay 230 asfollows: from ground by way of springs |69, conductor |66, and throughthe upper winding of relay 230 to bat-y tery. Relay 230, uponenergizing, at armature 23| opens the previously traced circuit formotor magnet |68, whereupon motor magnet |68 deenergizes to advance thewipers of the local finder into engagement with their next bankcontacts. The deenergization of motor magnet |68 also opens the circuitof relay 230 at springs |69, with the result that relay 230 nowdeenergizes. The deenergization of relay 230 again completes thepreviously traced circuit for motor magnet |68 and motor magnet |68again completes the circuit for energizing relay 230 to cause the latterrelay to open the circuit to motor magnet |68 and cause the latter Atostep the wipers into engagement with their next bank contacts. In thesame manner as just described magnet 68 and relay 230 operate until testwiper |53 encounters a calling potential of a calling line.

When test wiper |53 encountersr a bank contributor motor magnet 405 asfollows:

' nector links.

circuit may be traced as follows: from ground through the lower windingof relay 230, through the normally closed springs controlled by arma-,ture 226, lower winding of relay 220, conductor 220, bank contact andwiper 4|2, armature 40|, wiper 4|3' and engaged bank contact, conductor|03, test wiper |53 in engagement with the bank contact terminating thetest conductor of subscriber S', conductor armature |05, and through thelower Winding of relay |03 to battery. Relay 230 is maintained energizedover this circuit and relay 220, upon energizing, at armature 22|completes a circuit for energizing slow-to-release relay 2|0 by way ofarmature 23| and its working contact; at armature 222 prepares a pointin the circuit for energizing relay 280; at armature 223 prepares apoint in the circuit for energizing series relay 210; at armature 244connects ground to the guard lead 221 to make this nder connector linkbusy; at armature 225 connects ground to conductor |63 to maintain relay|03 in energized position and to busy the calling line in the banks ofthe finders; and at armature 226 connects the lower Winding of relay 230to the positive talking conductor and at the normally closed springscontrolled by armature 226 opens a point-in its own circuit through itslower winding.

Slow-to-release relay 2|0, upon energizing, at armature 2|| completesthe circuit for connecting relay 230 across the calling subscribersloop; at armature 2|2 completes a circuit through the upper winding ofrelay 220 to maintain this relay in energized position; at armature 2|3prepares a point in the connector test circuit; and at armature 2|4prepares a point in the impulsing circuit to the connector motor magnet351. Relay 230 is now maintained over the calling loop over thefollowing circuit: from ground through the lower winding of relay 230,armature 226, armature 20B, conductor |65, wiper |55, conductor |02 overthe calling subscribers loop to conductor |0|, wiper |5I, conductor|0l,`armatures 20| and 2| I, and through the upper winding of relay 230to battery. Line-cut-o relay |03 energizes over the previously tracedcircuit to operate armatures |04, |06 and |08 in their second step. Atarmatures |04 and |08 relay |03 disconnects the windings of relay |03and ground from the subscribers line conductors |0| and |02 and atarmature |06 disconnects ground from common start conductor 9.

When the start conductor 9 is no longer grounded, relay 420 deenergizesand at armature 42| opens the circuit to relay-400. At armature 422relay 420 again short circuits the resistance 423 to complete a circuitfor energizing the disfrom ground by way of the grounded start conductor221, bankY contacts and wiper 4|4, armature 422, interrupter springs 404and through the winding of motor magnet 405 to battery. This circuit isthe circuit by means of which the finder connector distributorpreselects idle nder con- Motor magnet 405 is intermittently energizedand deenergized over this circuit as long as wiper 4|4 encounters agrounded bank contact. Relay 400, upon deenergizing, at armature 40|opens a point in the finder test circuit; at armature 403 opens a pointin the circuit to the nder motor magnet |68; at armatheir fifth or stopposition contact.

ture 402 and its working contacts. opens the cir-v cuit oi.'slow-to-release Arelay 4|0; and at its resting contact completes acircuit by'way of armature 4|| for maintaining the motor magnet 405 inenergized position during the interval the slow-to-release relay 4|0 isenergized. MotorV magnet 405, upon energizing, Vpositions its pawlpreparatory to stepping the wipers of the'distributor and at interruptersprings 404 opens they preselecting circuit previously traced.Slow-torelease relay 4|0 deenergizes after an interval and at armature4|| opens the circuit vof motor magnet 405 whereupon the motor magnetdeenergizes and advances the wipers one step into engagement with thebank contact associated with the next nder connector link.

In case this finder connector link is busy there will be ground on theguard conductor corresponding to conductor 221, with the result that thepreselecting circuit tomotor magnet 405 is completed to cause the wipersto be set into engagement with the bank contact of the next finderconnector link. Motor magnet 405 is intermittently operated over itspreselecting circuit until wiper 4|4 no longer encounters a groundedguard conductor, thereby indicating an idle link. When wiper 4|4 losesground no circuit is completed for magnet 405 and therefore the wipersof the distributor stop in engagement with the bank contactassociated-with an idle finder connector link.

Incase all of the finder connector links are busy then each busy linkhas removed its individual ground from the common lead 2|6 to lprovide astop position for the wipers of the distributor to prevent theircontinuous operation during this busy condition. 'Ihis stop position isshown as the last or fifth position accessible to test wiper 4|4 andsuch position is normally grounded as long as any one of the iinderconnector links is idle. The circuit for grounding this position extendsfrom ground by way of armature 204, armature 2|3 and resting contact,conductor 2|0, to the stop position or fth bank contact accessible towiper 4|4. This stop position is therefore grounded as long as any oneof the links is idle and ground is removed therefrom only when all ofthe links are busy to provide a stop position for the wipers of thedistributor.

Considering now the case in which all of the nder connector links arebusy, then the wipers of the distributor would be in engagement with Incase a call is initiated at this time start relay 420 is energized overthe following circuit: from ground on the finder start conductor 9,through the winding of relay 420', armature 422, interrupter springs404, and through the winding of motor magnet 405 to battery. Relay 420alone energizes over this circuit; at armature 42| it completes acircuit for relay 400; and at armature 422 lremoves the short fromaround resistance 423, thereby inserting this resistance in series withrelayl 420. Relay 420 is therefore maintained over the circuit includingthe resistance 423 as long as the iinder start conductor 9 is grounded.

As soon as one of the iinder connector links becomes idle then the busycommon conductor 2| 6 is grounded, with the result that relay 420 isshort circuited from ground on the busy common conductor 2|6 extendingby way of Wiper 4|4 and ground on the start conductor 9. Magnet 405 ismarginal and will not energize in series with resistance 423 fromgrounded start conductor. When relay 420 deenergizes, said relay atarmature 422 completes the circuit for energizing magnet 405 over thefollowing circiit: from grounded busy common conductor 2|6, wiper 4| 4,armature 422, interrupter springs 404, and through the winding of magnet405 to battery. Magnet 405 intermittently operates until test wiper 4I4nds the idle connector link.

Considering now the case in which all of the finder connector links arebusy and the distributor wipers are in stopping position, it will now beassumedthat one of the links becomes idle at a time when no call isbeing made. In this case as soonas the busy common conductor 2|6 isgrounded the circuit for energizing motor magnet 405 is completed by wayof wiper 4|4 and armature 422. Magnet 405 operates in the same manner aspreviously described until the wiper 4|4 flnds the idle connector link.

Returning now to the link circuit at a time when the calling line isfound and relays 220 and 2I0 have been operated, dial tone is connectedby the operation of these relays to the calling subscribers line asfollows: from dial tone conductor 390, twenty-fifth bank contact ornormal position of connector wiper 356 and said wiper, conductor 239,resting contact and armature-253, the tone condenser TC, lower talkingcondenser, and from thence over the calling substation loop aspreviously traced for relay 230. When the calling subscriber hears thewellknown dial tone, such subscriber will dial the number assigned tothe desired subscriber, which number may comprise one, two, or threedigits. Assuming now that subscriber S desires to be connected tosubscriber S' shown in Fig. 3, and since the number of subscribers S is6, the calling subscriber will thereupon dial the digit 6". In responseto the operation of the calling device CD in accordance with the digit 6the circuit to line relay 230 is interrupted six times, thereby causingthe line relay 230 to be deenergized a corresponding number of times.Relay 230 thereupon deenergizes for each impulse and at armature 23| andits resting contact temporarily opens the circuit to slow-to-releaserlay 2 0, which, however, is slow to deenergize and is thereforemaintained energibed during the impulsing period. At armature 23| andresting contact, relay 230 transmits an impulse to the connector motormagnet 351 upon each deenergization. This circuit may be traced asfollows: from ground by way of armature 205, armature 23| and restingcontact, armature 2|4, armature 252, armature 296, conductor 235, andthrough the winding of relay 351 to battery. A branch of this circuitextends from armature 296 by way of armature 223 and the lower windingof series relay 210 to battery for energizing the latter relay duringthe impulsing period.y

Connector motor magnet 351, upon energizing, positions its pawlpreparatory to stepping the wipers of the connector. Relay 210, uponenergizing, at armature 21| opens a point in the circuit to relay 200;at armature 212 opens a point in the circuit to switching relay 290, andalso prepares a point in the circuit for combined busy and back bridgerelay 250; at armature 213 short circuits its upper winding to make thisrelay slow-to-release so that it will be maintained in energizedposition during the impulsing period; and at armature 214 closes a shuntaround armature 252 to prevent the operation of busy relay from openingthe impulsing circuit to the motor magnet 351. When relay 230 energizesafter each impulse, the circuit to connector motor magnet 351 is opened,with the result that thisA magnet steps the wipers of the connector onestep for each deenergization. In response to the six impulsestransmitted thereto, magnet 351 steps the wipers of the connector fromin engagement with their normal bank contacts into engagement` with,their sixth bank contacts, or the contacts terminating the called line.

The operation of the finder connector at this time depends upon whetherthe called line is busy or idle. In case the called line is busy, thenground will be encountered by test wiper 353, with the result that` thecombined busy relay and back-bridge relay 250 is energized over thefollowing circuit: from ground on the busy test conductor of the calledline, sixth bank contact engaged by wiper 353, conductor 234, armature212 and working contact, armature 295, resistance 254, and through theupper winding of relay 250 to battery. At armature 25| relay 250 opens apoint in the testing circuit extending through the upper winding ofswitching relay 290 and at its working contact prepares a lockingcircuit for busy relay 250. At armature 252 relay 250 opens a point inthe impulsing circuit to magnet 351 and at armature 253 connects thebusy tone to the calling line. Shortly after the impulses cease seriesrelay 210 deenergizes and at the normally closed springs controlled byarmature 212 completes the locking circuit for busy relay 250 asfollows: from ground by way of armature 204, armature 2|3 and workingcontact, armature 25| and working contact, through the normally closedsprings controlled by armature 212, armature 295, resistance 254, andthrough the upper winding of busy relay 250 to battery. The busy tone istransmitted to the calling subscriber over the following circuit: from abusy tone, armature 291, working contact and armature 253, tonecondenser TC, lower talking condenser, and thence over the heavy talkingconductors to the calling line.

When the calling subscriber hears the busy tone, such subscriber willreplace his receiver to cause the release of the established connectionin a manner to be more fully described hereinafter.

Assuming now that the called line was idle instead of busy, then nocircuit is completed for busy relay 250 because the test conductor ofthe called line is not grounded. Series relay 210 deenergizes shortlyafter the impulsing period and at armature 212 completes the circuit forenergizing the switching relay 290 in series with line-cut-off relay 303of the called line as follows: from ground by way of armature 204,armature 2|3 and working contact, armature 25| and resting contact,through the upper winding of switching relay 290, resting contact andarmature 212, conductor 234, test wiper 353 in engagement with its sixthbank contact, conductor 3|0, and through the lower winding of two-step,line, andcut-oi relay 303 to battery.

Relay 303 energizes over the above-traced circuit and operates itsarmatures in their second step to disconnect itself and ground from theline conductors of the called line. Switching relay 290, uponenergizing, at armature 292 prepares a point in the transfer circuit; atarmature 293 completes a locking circuit through its lower winding byWay of armature 283 and grounded armature 2|2; at armature 294 connectsdirect ground to wiper 353 to mark the called line busy to otherconnectors having access thereto; at armature 295 opens a point in thecircuit to busy relay 250; at armature 296 opens a point in theself-restoring circuit of connector motor magnet 351; at armature 291opens a point in the busy tone circuit; and at armatures 29| and 298connects interrupted generator to the'called line. The.circuit forsignalling the called subscriber may be traced as follows: frominterrupted generator by way of resting contact and armature 263,armature 296, conductor 239, wiper 356 in engagement with its.

sixth bank contact, conductor 302, through the ringer bells RB andringing condenser at the substation, over conductor 30| and from thenceto the sixth bank contact engaged by wiper 35| and said wiper, conductor232, armature 29|, armature 26| and resting contact, and through theupper winding of ring-cut-off relay 260 to battery.

When the called subscriber answers, ring-cutofi relay 260 is energizedover the called subscribers loop, this time including the transmitter Tand the upper switchhook springs SH in place of the ringer RB and theringing condenser. At armature 262 relay 260 completes a locking circuitthrough its lower winding from grounded armature 2|2 and at armatures26| and 263 opens the ringing circuit and-at the working contacts ofthese armatures connects the called line in series with differentialrelay 244 and relay 250.

Relay 250 is energized over the called subscribers loop as follows: fromground by way of armature 2|2, armature 262, through the lower windingof relay 250, through the lower winding of diilerential relay 244,working contact and armature 263, from thence over the previously tracedcircuit through the called subscribers loop to armature 29|, armature26| and Working contact, through the upper Winding of differential relay244 and through the upper winding of relay 250 to battery. Relay 250alone is energized over this circuit and furnishes talking batterythrough both its windings to -the called subscriber. Diierential relay244 does not energize over the previously traced circuit because the twowindings are equal and oppose each other. The talking circuit betweenthe local subscribers lines are noW completed over the heavy talkingconductors.

After conversation and responsive to the calling subscriber S replacinghis receiver, line relay 230 deenergizes when its circuit is opened atthe switchhook springs SH and said relay at armature 23| opens thecircuit to release relay 2lb. After an interval slow-to-release relay2|0 deenergizes and at armature 2H opens a point in the talking circuitto the calling line. At armature 2l3 relay 2|0 connects groundedarmature 204 to the busy common conductor 2|6 to prevent the iinderconnector distributor from stopping on its stopping position aspreviously described, and at armature 2|2 opens the holding circuits ofrelays 290, 260, and 220. Relay 220, upon deenergizing, at armature 224removes one of the multiple ground connections from guard conductor 221,which conductor at this time is grounded by connector wiper 354 inengagement with its multiple contacts connected to ground. At armature225 relay 220 disconnects ground from conductor |63 and test wiper |53to remove the busy guarding potential, and at armature 226 opensafurther point in the talking circuit and prepares the circuit throughthe lower winding of relay 220.

Switching relay 290, upon deenergizing, at armatures 29l and 298 openspoints in the talking circuit to the called line and the circuit ofrelay 250 in case the called subscriber has not replaced his receiver;at armature 293relay 290 opens its own locking circuit; at armature 294opens the circuit to line-cut-oi relay 303 and removes the busy groundpotential; and at armature 296 completes a self-restoring circuit forthe connector. This self-restoring circuit may be traced as follows:from ground by way of the multipled contacts engaged by wiper 354,conductor 221, armature 224 and resting contact, conductor 231,interrupter spring 358, conductor 236, armature 296, conductor 235, andthrough the winding of magnet 351 to battery. At interrupter springs 358motor magnet 351 interrupts its own circuit to cause the magnet tooperate in the same manner as a buzzer to advance the wipers step bystep until wiper 354 no longer encounters a grounded bank contact. Sincethe normal position bank contact accessible to wiper 354 is the onlybank contact accessible to this wiper that is not grounded, the wipersof the connector will be advanced step by step by motor magnet 351 untilwiper 354 reaches its normal position. When wiper 354 reaches its normalposition, ground is removed from guard conductor 21 to permit thisfinder connector link to be preselected by the finder connectordistributor shown in Fig. 4.

The local subscribers are divided into three groups, the rst grouphaving only a single call digit in their telephone numbers, the secondgroup having two call digits in their telephone numbers, and the thirdgroup having three digits in their telephone numbers. The first digit inthe telephone numbers of all second-group subscribers is the digit 0,and the rst and second digits of the subscribers telephone numbers inthe third group are the digits 0-0.

In order to call a subscriber in the second group the calling subscriberinitiates the callin the same manner as previously described to cause ander-connector link to be connected to the calling line. ln response todial tone the calling subscribed dials the digit "0 to step theconnector to the tenth bank contacts, which contacts are dead contactsand do not complete any circuits. Since neither ground nor battery isencountered by test wiper 253, the connector remains in this positionuntil the receipt of the second digit. In response to the callingsubscriber dialling the second digit the wipers of the connector arestepped from the tenth bank contacts a number of steps corresponding tothe digit dialled and into engagement with the bank contact terminatingthe called line in the second group. The connection is now completed bythe connector in the same manner as previously described. .in order tocall a subscriber in the third group the calling subscriber dials thedigit 0 for the rst digit, the digit 0 for the second digit, and thenthe units digit of the called line to cause the wipers of the connectorto come to a rest in engagement with the bank contacts terminating thecalled line.

Incoming calls It will now be assumed that an incoming trunk call isreceived over conductors 194 and 195 from the distant exchange. When anincoming call is received over conductors 194 and 105, relays and 180operate. Relay 180 is a very high Wound relay and operates in responseto either the ringing current or during the silent period, while relay110 is an anternating current relay which operates only in response toringing current. The circuit for energizing alternating current relay110 may be traced as follows: from generator at the main exchange,conductor 194, condenser and upper winding of alternating current relay110, resting Contact and armature 113, conductor 694, armature `666,conductor 695, armature 144, conductor 195', back to generator at themain exchange. Relay 180 is energized over the following circuit: fromground at the main exchange, or generator, extending over conductor 194through the winding of relay 180, armature 144, and by way of conductor195 back to main exchange battery. At armature 18| relay 180 completesan obvious circuit for energizing slow-to-release relay 150. Relay 110,upon energizing, at armature 11| prepares a point in its own lockingcircuit; at armature 112 disconnects ground from conductor 314- to markthis trunk as calling in the bank of the trunk distributor shown in Fig.3; at armaturer112 and working contact grounds conductor 310 to energizerelay 3|4 over an obvious circuit; at armature 113 and resting contactdisconnects the upper winding of relay 110; and at its working contactbridges the alternating current signalling relay 160 and condenser Cacross the trunk conductors 194 and 195 by way of armatures 666 and 144and conductors 694 and 695.

Relay 150, upon energizing, at armature 15| completes a circuit forenergizing slow-to-release relay 190; at armature 152 completes acircuit for energizing relay at armature 153 prepares a point in its ownlocking circuit; at armature 154 completes the locking circuit throughthe lower winding of relay 110 by way of armatures 623 and 633 and theirresting contacts over conductor 628; and at armature 155 prepares asubstitute circuit for alternating current signalling relay 160. Atarmature 19| and its resting contact relay 190 disconnects one of theground connections from the busy common conductor 316 over which thebusy relay 36| is normally held energized as long as one of the trunklines is idle. At armature 19| and its working contact relay 190connects ground to conductor 313 to operate the trunk distributor incase the wiper 335 is in engagement with the bank contact terminating inthis particular conductor. At armature 192 relay 190 prepares a point inthe circuit for energizing relay 630. Relay 130, upon energizing, atarmature 13| disconnects relay 120 and prepares a point in the talkingcircuit; at armature 132 connects another ground to relay 192; and atarmature 133 prepares a point in its own locking circuit. Relay 3|4,upon enenergizing, at armature 320 disconnects ground from conductor 31|to remove the busy condition and connects battery through the windingsof relays 3|5 and 3|6 to the trunk answering bank'contact No. 8 in theconnector bank accessible to wiper 353.

Alternating current signalling relay operates from ringing currenttransmitted from the main exchange and at armature 162 maintains thecircuit of relay 150 independent of armature 18|. At armature 16|alternating current signalling relay 160 connects battery to conductor624, through resistance 163, to signal the attendant or to operate thecommon trunk signal lamps located throughout the premises dependent uponwhether the attendant signal key SK is operated or at normal. r

Assuming that the key SK is normal, then relay 501 is energized over thefollowing circuit: from ground through the winding of relay 501,normally closed springs of key SK, common conductor 609, resting contactand armature 662, conductor 624, armature 16|, and through resistance163 to battery. At armature 508 relay 501.A completes the circuit forlighting the trunk signal lamps located throughout the premises toenable the non-restricted subscribers to answer the incoming trunk call.

The trunk distributor shown in Fig. 3 is arranged to normally preselectan idle trunk for use in'an outgoing call, and in case the outgoing testwiper 335 is in engagement with the bank contact terminating conductor313 of the trunk shown in Fig. '1 when such trunk is seized for anincoming call, the trunk distributor motor magnet 333 is energized asfollows: from grounded conductor 313, bank contact and Wiper 335,resting contact and armature 322, armature 328, interrupter springs 334,and through the winding of motor magnet 333 to battery. Motor magnet 333operates to position the pawl preparatory to stepping the wipers of thedistributor and at its interrupter springs 334 interrupts its owncircuit. Magnet 333 thereupon deenergizes and advances the wipers of thedistributor into engagement with the bank contacts terminating the nexttrunk line. In case this trunk line is idle, wiper 335 does notencounter a grounded bank contact and the Wipers remain in thisposition. In case the next trunk line is busy, then ground isencountered by the wiper 335 to again advance the wipers to the nexttrunk or until an idle trunk is found.

Any non-restricted local subscriber equipped with a push-button, such asPB, may answer this trunk call by removing his receiver and dialling thedigit 8 to position the connector of the lnder-connector link on thetrunk answering position 8.

In response to subscriber S removing his receiver to answer this trunkcall, an idle nder connector link is connected to this subscriber's lineand in response to the receipt of dial tone such subscriber will dialdigit 8 to answer the trunk call. In the same manner as previously vdescribed the connector wipers are stepped into engagement with theireighth bank contacts and when series relay 210 deenergizes after theimpulsing period a circuit is completed for energizing relays 290 and3|6 in series as follows: from ground by way of armature 204, armature2|3 and working contact, armature 25| and resting contact, through theupper winding of switching relay 290, resting contact and armature 212,conductor 234, test wiper 353 in engagement with its eighth bankcontact, conductor 31|, armature 320 and its working contact, throughthe winding of marginal relay 3|5 and through the upper and lowerwindings of relay 3 |6 to battery. Relay 3|5 is marginal and will notoperate in series with the lower high-resistance winding of relay 3| 6.Relay 290, upon energizing, at armature 292 prepares a point in thecircuit for the local release relay 200 and for marking the line ofsubscriber S as answering a trunk call in the trunk finder bank. Atarmature 293 relay 290 again completes its locking circuit and atarmature 294 grounds test wiper 353. Relay 3|6, upon energizing, atarmature 326 opens the initial energizing circuit for relay 363 toprevent its operation in case an outgoing call is originated before theincoming call is completed. At armature 325 relay 3|6 completes acircuit for shunting out the lower high-resistance winding of relay 3|6only in case\ relay 363 is not energized in a preceding outgoing call.When the lower Winding of relay 3l6 is shunted by battery at amature369, marginal marking relay 3|5 thereupon energizes in series with relay3|6. Relay 3|5, upon energizing, at armature 32| grounds conductor v312for a purpose to be described`later; at armature 322 switches the testcircuit from the outgoing test Wiper 335 to the incoming test wiper 336Vto cause the trunk distributor to nd the calling trunk. At armature 323relay 3|5 grounds conductor 386 to prepare a circuit for the localrelease relay 266 and likewise' marks the line answering this trunkcall, or line S, in the trunk iinder bank.

At armature 324 relay 3|5 closes a circuit for energizing relay 3|1 whenthe calling trunk is found by the trunk distributor.l

Considering now that the wipers of the trunk distributor are in theposition shown in the drawings, thenrelay 3|1 is short circuited fromground encountered on the multiple contacts by wiper 336 by way ofarmature 322 and armature 324. A branch of this circuit extends by Wayof armature 328 and interrupter springs 334 through the winding of motormagnet 333 for operating Ithe latter magnet. In the same manner aspreviously described, magnet 333 steps the Wipers of the trunkdistributor and interrupts its own circuit until wiper 336 no longerencounters agrounded contact, or in this case until wiper 336 encountersthe contact terminating conductor 314, from which ground has beenremoved by the operation of relay 116. It should possibly be stated atthis time that the motor magnet 333 is marginal and will not energize inseries with either resistance 329 or the winding of relay 3|1.

When wiper 336 no longer encounters a grounded bank contact, the shortcircuit around relay 3|1 is removed, with the result that this relay nowenergizes over the following circuit: from ground by way of armature324, winding of relay 3|1, armature 328, interrupter springs 334, andthrough the Winding of magnet 333 to battery. Relay 3|1 alone energizesover this circuit and at armature 321 completes a circuit for energizingrelay 3|8, and at armature 328 removes the short circuit from aroundresistance 329 to prevent the energization of magnet 333 in caseconductor 314 becomes grounded. At armature 336 relay 3|8 completes acircuit for energizing relay 3 I 9 and at armature 33| grounds conductor629 to energize relay 656 in the trunk. At armature 332 relay 3|9prepares a point in the circuit for magnet 333. Y

'Ihe circuit for energizing relay 6,56 may be traced as follows: fromground by Way of arma-g ture 33|, wiper 331 in engagement with its sixthbank contact, conductor 629, and through the winding'of relay 656 tobattery. At armature 65| relay 656 prepares a circuit for latermaintaining relay 616 in energized position; at armature 652 preparesthe trunk test circuit for energizing relays 610, 666, and 266 inseries; at armature 653 disconnects a point in the transfer circuit; atarmature 654 completes a circuit for energizing the trunk finder motormagnet 568;

and at armature 655 prepares apoint in the bridge across conductors 56|and 565. The circuit for energizing magnet 568 may be traced fromgrounded armature 654 by way of armature 61| and resting contact,conductor 561, and through the winding of trunk iinder motor magnet 568to battery.

Motor magnet 568 energizes and positions its pawl preparatory tostepping the wipers of the trunk nder and at its springs 569 completesthe circuit for energizing relay 616 over the following circuit: fromground by way of springs 569, conductor 566, and through the upperwinding of stepping relay 616 to battery. Stepping relay 616 energizesover the above-traced circuit and at armature 61| and its restingcontact opens the circuit to the trunk finder motor magnet 568 and atits working contact connects another ground to conductor 692. Motormagnet 568 deenergizes when its circuit is opened by relay 610, and,upon deenergizing, advances the Wipers of the trunk nder one step andlikewise opens the circuit of stepping relay 616 at springs 569. Atarmature 61| stepping relay 616 again completes the circuit forenergizing motor magnet 566 and the motor magnet 56B at springs 569again completes the circuit for stepping relay 616. Motor magnet 568 andstepping relay 616 intermittently operate as described until test wiper552 of the trunk iinder finds the marked bank Contact, at which time acircuit is completed for energizing relays 266 and 666 as well asmaintaining stepping relay 610 in energized position. This circuit maybe traced as follows: from ground by Way of armature 323, conductor 386,eighth bank contact engaged by wiper 352 and said Wiper, conductor 233,armature 282 and resting contact, armature 292, lower winding of localrelease relay 266, conductor |62, Wiper |52 in engagement with itsfifteenth bank contact or the bank Contact corresponding to the callingline answering this trunk call, conductor '28, fifteenth bank contact inthe trunk nder accessible to wiper 552 and said Wiper, conductor 562,resting Contact and armature 62|, armature 652, through the upperwinding of relay 666 and through the lower Winding of stepping relay 616to battery.

Stepping relay 616 is maintained energized I over this circuit andrelays 266 and 666 are energized thereover. At armatures 66| relay 666completes a circuit by way of armature 65| through the upper winding ofstepping relay 616 for maintaining this relay in energized position; andat armature 662 and resting contact opens a point in the circuit foroperating the' signal relay 561. At armature 663 relay 666 completes acircuit by Way of resting contact and armature 663 for energizingslow-to-operate relay 696; at armature 664 completes a circuit forenergizing slow-to-release relay 636; and at armature 665 connectsconductor 693 to conductor 696 to provide another circuit for signalrelay '|66 when armatureA 666 disconnects conductor 694 from 695. Thecircuit for energizing relay 636 may be traced from grounded conductor692 grounded at either armature 162v or by way of armatures 654 and 61|and thence by Way of armature 664 through the winding of relay 636 tobattery. At armature 63| relay 636 closes a point in the upper talkingconductor; at armature 632 opens a point in the circuit to relay 646 atarmature 633 closesacircuit for maintaining relay 666 energized throughits lower winding from grounded armature 623; at armature 634 groundsconductor 564 and wiper 554 to make the line answering this trunk callVbusy and for holding the combined line and cut-off relay |03 inenergized position; at armature 635 completes a bridge across conductors56| and 565 including the resistance 631 and armature 655; and atarmature 636 closes a point in the lower talking conductor.

In the local finder connector link local release relay 200 energizes inseries with relay 660 and at armatures 20| and 206 opens the lineconductors extending to line relay 230, whereupon the latter relay nowdeenergizes. At armature 203 relay 200 closes a locking circuit throughits upper winding as long as slow-to-release relay 2|0 remainsenergized; at armature 204 opens a point in the original energizingcircuit of relay 290 or the locking circuit of the busy relay 250 if thelatter relay is energized; and at armature 205 opens a point in theimpulsing circuit and also opens the circuit of relay 2|0. Relay 230deenergizes and at armature 23| opens a further point in the circuit ofslow-to-release relay 2|0. After an interval slow-to-release relay 2|0deenergizes to cause the deenergization of switching relay 290and causesthe connector to release in the same manner as previously described.

When relay 290 deenergizes and at armature 204 removes ground from wiper353, the circuit to relays 3|5 and 3|6 is opened, causing the latterrelays to dcenergize. Relay 3|6 deenergizes and at armatures 325 and 326allows other trunk calls to be originated and answered. Relay 3|5deenergizes and disconnects ground from conductor 312. At armature 322relay 3|5 disconnects the incoming test wiper 336 and connects up theoutgoing test wiper 335 to cause the trunk distributor to hunt for andselect an idle trunk. At armature 323 relay 3|5 disconnects markingground from conductor 380 to open the original energizing circuit ofrelays 200 and 660; and at armature 324 opens the circuit to relay 3 1which now deenergizes. At armature 321 relay 3|1 opens the circuit ofrelay 3|8 which now deenergizes and at armature 328 short circuits theresistance 329 to permit the energization of magnet 333. At armature 330and its working contact relay 3|8 opens the circuit of s1owtoreleaserelay 3|9 and at its resting contact completes a circuit for energizingmotor magnet 339 by way of armature 332 as long as the slow-to-releaserelay 3|9 is operated. At armature 33| relay 3|8 removes ground fromconductor 629 to cause the deenergization of relay 650. Slow-to-releaserelay 3|9 deenergizes after an interval and opens the circuit of motormagnet 333 at armature 332, thereby causing the magnet upon itsdeenergization to advance the wipers into engagement with the next bankcontact. Since the outgoing test wiper 335 is connected to the groundedmultiple contacts at this time, the magnet 333 intermittently operatesas previously described to step the wipers of the trunk distributor insearch of an idle trunk.

Assuming that the trunk last used, was the last available trunk thenground is disconnected from the busy common conductor 316 to provide astopping position for the trunk distributor wipers to prevent theircontinuous operation as long as all of the trunk lines are busy.Assuming, however, that one or more of the trunk lines are idle, thenbusy common conductor 316 is grounded and the wipers are advanced untiltest wiper 335 loses ground, such condition indicating an idle trunk.The normally energized alltrunk-busy relay 36| also deenergizes when allof the trunks are busy when ground is removed from. the busy commonconductor 316. At annature 364 relay 36| opens the circuit to relays 362and 363 to prevent their energization when a local subscriber attemptsto originate an outgoing call, and at the resting contact of armature364 grounds the ninth bank contact acces- 318 was not grounded and theconnector of a nder connector link switches through to cause theseizure,of the last idle trunk. At the same time, however, the trunk wasseized for an incoming call and therefore since incoming calls are givenpreference over outgoing calls the party originating the outgoing callis given a busy tone over conductor 311.

When relay 630 energizes in response to the operation of relay 660 atthe time the trunk nder nds the answering local line, relay 630 rstoperates its preliminary make armature 635 before operating its otherarmatures to close a ring-cut-otf bridge across the upper and lowertalking conductors extending to the distant main exchange. Thisring-cut-oi bridge, comprisingarmature 63|, resistance 631, andarmatures 655, 635, and 636 is only temporarily placed across the trunkconductor to cause the disconnection oi ringing current at the mainexchange in the well-known manner and to reduce the click in theanswering subscribers receiver, since the subscribers line at this timeis also connected in bridge of the trunk line. The operation of armature633 at its resting contact also opens the locking circuit of relay 110which deenergizes to open the circuit of relay 3|4 at the workingcontact of armature 112, and to ground the marking conductor 314 at theresting contact of armature 112. Relay 3|4 deenergizes and at armature320 opens the circuit to relays 3|5 and 3|6 and grounds conductor 31| toplace busy potential on the answering trunk position terminating in theeighth bank contact accessible to wiper 353.

When relay 650 deenergizes in response to the deenergization of relay3|8 relay 650 at armature 65| opens the circuit of relay 610 whichthereupon deenergizes, at armature 652 opens the test circuit throughthe relays 660 and 610; at armature 654 opens a point in the circuit tomotor magnet 56B to prevent its operation; and at armature 655 opens thering-cut-off bridge previously referred to. Relay 610 deenergizeswithout result since the circuit to motor magnet 568 is opened atarmature 654.

At this time the local finder connector link has released and isavailable for use in other local calls, while in the trunk circuit shownin Figs. 6 and 7 the following relays are operated: relays 630, 660,690, 130, 150, 180, and 190. The line of substation S is now connectedto the distant main exchange over the following circuit: from thesubstation S, conductors 0| and |02 terminating in the trunk finderbank, wipers 55| and 555, conductors 56| and 565, armatures 63| and 636,through the upper and lower windings of differential relay 6|4,conductors 6|6 and 691, through the normally closed springs controlledby armatures 10| and105 through the talking condenser and through theupper and lower windings of series relay 1| 3 in multiple, restingcontact and armature 123, working contact and armature13l, and overtrunk conductors 194 and 195 to the distant main exchange.

Relay 6|4 in the circuit just traced is a differential relay andtherefore does not operate its armature when both windings areenergized. Series relay 1|3 energizes over the above traced circuit andat amature 1|4 completes the circuit for energizing relay 140. Atarmature 14| relay maintains relay 196 energized, at armature 142completes a locking circuitfor relay 130, at armature 143 completes alocking circuit for relay 150, and at armature 144 disconnects relay 180from in bridge of trunk conductors 194 and 195 to cause the latter relayto deenergize. The deenergization of relay 180 is without effect at thistime since relay is now held energized over its locking circuit.Subscriber S now converses with the calling subscriber over the heavytalking conductors and both the calling and the called subscribersreceive their talking battery from the main exchange.

The release of incoming trunk connections is under control of thecalling main-exchange subscriber or the main-exchange operator. Thereplacement of the receiver by subscriber S opens 'the circuit of seriesrelay 1|3 which accordingly deenergizes and opens the circuit of relay140. At armature 144 relay 146, upon deenergizing, reconnects the highresistance relay 180 across the trunk conductors to cause itsenergization if the calling main-exchange subscriber has not hung up. Atarmature 18| relay 180 maintains slow to release relay 150 operated toprevent the deenergization of relay 130. If the distant main-exchangeoperator desires to re-signal subscriberl S she may do so by applyingringing generator to the trunk conductors 194 and 195. The alternatingcurrent signalling relay reoperates over a circuit including armatures155 and 665, but does not operate the general trunk signals because thesignalling circuit is open at armature 662. Ringing current transmittedfrom the main exchange extends over the talking circuit previouslytraced to the line of subscriber S to operate the ringer RB at thissubstation and therefore directly signal subscriber S.

When the distant calling subscriber or the distant operator disconnectsat the main exchange, relay deenergizes and at armature 181 opens thecircuit to slow-release relay 150. At armature 15| relay 150, upondeenergizing, opens one of the circuits extending to relay at armature152 opens thecircut to relay 130 which now deenergizes; and at armature155 opens the circuit of alternating current signalling relay 160. Atarmature 13| relay 130, upon deenergizing, opens a point in the talkingcircuit and at armature 132 opens the circuit of slowto-release relay'|90 which now deenergizes. At armature 19| relay 190 grounds the busycommon conductor 316 and disconnects ground from conductor 313 to allowthis trunk to be used in an outgoing call. At armature 192 relay 190opens the circuit of relay 630 which now deenergizes. At armatures 63|and 636 relay 639 opens a further point in the talking circuit; atarmature 633 opens the circuit of relay 660 which deenergizes; and atarmature 634 removes the busy ground from the multipled test conductorof the called line and likewise causes the release of the combined lineand cut-off relay |03. At armature 662 relay 660, upon deenergizing,reestablishes the signalling circuit for operating Outgoing calls Anynon-restricted, local subscriber may originate an outgoing trunk call byremoving his receiver and dialling the digit 9 to position the connectorora local finder connector link on the trunk calling position 9. Inresponse to the subscriber S removing his receiver to originate a trunkcall, an idle nder connector link is connected to this subscribers lineand, in response to the receipt of dial tone, subscriber S dials thedigit 9 to operate the connector wipers into engagement with their ninthbank contact in the same manner as previously described.

In case all of the trunks are busy, then busy relay 36| in the trunkdistributor is deenergized and ground is connected to trunk callposition 9 engaged by wiper 353 to causel the operation of the busyrelay in the local iinder connector link. The operation of the busyrelay, such as relay 250 in the link shown in Fig. 2, causes the busytone to be transmitted to the calling line in the same manner aspreviously.

In case, however, one or more of the trunks are idle, then the busyrelay 36| is in energized position and a circuit is completed forenergizing the switching relay, such as switching relay 290 in thefinder connector link, in series with relays 362 and 363 in case thetrunk distributor is not in use answering an incoming trunk call. Relay362 is marginal and will not energize in series with the upper windingof relay 363. The circuit for energizing switching relay 290 and relay363 may be traced as follows: from ground by way of armature 264,armature 2|3 and working contact, armature 25| and resting contact,through the upper winding of switching relay 290, resting contact andarmature 212, conductor 234, test wiper 353 in engagement with its ninthbank contact, conductor 316, armature 364 and its working contact,through the winding of marginal relay 362, through the lower and upperwindings of relay 363, to battery at armature 326.

In case the trunk distributor is in use in answering an incoming trunkcall, relay 3|6 is operated and the circuit just traced is not completeduntil relay 3|5 deenergizes as previously described. At armature 369relay 363 shunts out the upper high-resistance winding of relay 363 topermit the energization of marginal marking relay 362. In a similarmanner the operation of armature 369 prevents'the operation of marginalmarking relay 3|5 in case some subscriber subsequently attempts toanswer an incoming-trunk call when the trunk distributor is in use.Relay 362, upon energizing, at armature 361 marks the calling line inthe banks of the trunk finders over the following circuit: from groundby way of armature 361, conductor 319, ninth bank contact and wiper 352,conductor 233, armature 282 and resting contact, armature 292, throughthe lower winding of local release relay 200, conductor |62, Wiper |52,conductor 28 multipled to the trunk finders to the fifteenth bankcontact accessible to wiper 662. At armature 363 relay 362 completes thecircuit for energizing relay 3|1 over the following circuit: from groundby way oi armature 363, winding of relay 3|1,

yarmature 323. interrupter springs 334, and

' has therefore preselected the trunk shown in Figs. 6 and 'I when theoutgoing trunk call was originated.

l In case the wiper 336 was in engagement with a grounded bank contact,the relay 3|1 would have been short circuited to prevent its operationand the motor magnet would have operated the wipers oi the trunkdistributor until an idle trunk was found. At amature 321,relay 3I1operates relay 3|9 and at armature 326 opens the short circuit aroundresistance 329.' At armature 33,6 relay3|6 completes the circuit forrelay Ill' and at armature 33| completes the circuit ior energizingrelay 666 in the preselected idle trunk as'follows: from ground by wayoi.' armature 33|', -wiper 331'in engagement with its nrst bank contact,conductor 629 and through the winding of relay 660 to battery. I

In response to the operation of relay 660,' the trunk finder is operatedin the same manner as previously described to rind the marked bankcontact. at which time a circuit is completed for energizing the localrelease relay 290 in thc finder connector link and relay 660 in thetrunk aswell as maintaining relay 610 in operated position. Theoperation of the relay 666 in the same manner as previously describedcauses the operation of relays 690 and 636; In the local armature 325.At armature 3 61 the ieenex'giza-V finder connector link local releaserelay 260 is energized and Tcauses the local ilnder connector link torelease in the same manner as previously described. When switching relay290 in the local finder' connector link, deenergizes, ground is removedfrom wiper 363, thereby opening the circuits of relays 362 and 363. Atarmature 369 relay 363 now permits any incoming calls to be answered byconnecting battery to tion ot relay 362 disconnects marking' ground fromconductor 319. At armature 396 relay 362 opens the circuit of relay 3l1which deenergizes to allow the motor magnet to step the wipers of thetrunk distributor in search of an idle trunk.

At armature 33| relay lll, upon deenergizing, opens the circuit of relay666.

The operation of the trunk relays are slightly dii'ferent dependent uponwhether the trunk conductors 194 and 196 extend to a manual or anautomatic exchange. In either case, ground is disconnected from trunkconductor 194 at the main exchange, while conductor 195 extends to asignalling relay and negative battery in case oi' a manual exchange orextends through the line relay'of an incoming line switch in case themain exchange is an automatic exchange. In addition, relay 120 in Fig.'l is permanently short circuited in case the trunk conductors 194 and196 extend to an automatic exchange. while the short circuit is removedfrom around said relay ln case the trunk conductors extend to a manualexchange. Y

It will ilrst be assumed that the trunk conductors extend to a manualexchange and thereu tore a circuit may be traced from ground through thewinding of relay 120 through the local cainng subscribers loop and fromthence through the signalling relay at the main manual exchange tobattery. The circuit for energizing relay 120 may. be traced in detailas follows: from ground through the winding of relay 120, normallyclosed springs controlled by armature 13|, through the upper winding ofseries relay 1l3,y normally closed springs controlled by armature 10|,conductor 6|6, through the upper winding oi.' diilerential relay 6|4,armature 63|, resistance 631, armature 666, armature '636, varmature636, through the lower winding of differential relay 6l4, conductor 691,normally closed springs lcontrolled by armature 106, through the lowerwinding of series relay 1|3, resting contact and armature 123, and overconductor 196 to battery through the signalling relay at the mainexchange.

'Ihe calling subscribers loop is also connected across the talkingconductors 56| and 565 to assist in energizing relays 120 and 1|3 and tolater on maintain series relay 1I3 in energized position after thebridge including resistance 631 and armatures 666 and 636 is opened. Theoperation of the signalling relay at the main exchange signals theoperator thereat in the wellknown manner. Series relay 1|3, uponenergizing over the above-traced circuit, at armature 1l4 completes anobvious circuit for energizing relay 140. Relay 120, upon energizingover the above-traced circuit, at armature 12| likewise completes acircuit for energizing relay 140; at armature 122 completes a circuitfor connecting battery through resistance 124 through the lower windingof series relay 1|3 before armatures 12| and 123 are fully operated, inorder to maintain the series relay 1|3 in energized position when relay120 subsequently deenergizes. At armature 123 relay 120 connects directground to conrluctory |96 to maintain the main-exchange signalling relayin energized position. Slow-torelease relay 140, upon energizing, atarmature 14| completes an obvious circuit for energizing relay 190; atarmature 142 prepares a point in the circuit for relay 130; at armature143 prepares a point in the locking circuit for relay 150; and at'armature 144 disconnects relays 110 and 160 from in bridge of the trunk.Relay 190, upon energizing, at armature 19| and its resting contactdisconnects one of the ground connections to the busy common conductor,and at its working contact grounds conductor 313 to short .circuit relay3|1 and cause the trunk distributor 1 to preselect another trunk aspreviously described.

At armature 192 relay 190 completes a circuit for holding relay 630 inenergized position by way ol.' conductor 692 and armature 664.

When the trunk distributor operates in the manner previously describedto preselect an idle trunk, the circuit to relay 650 is opened,whereupon sueh relay now deenergizes. At armatures and 662 relay 650opens the circuit to relay 610 which now deenergizes; at armatureA 654opens the original energizing circuit oi' relay 690, which relay is nowheld energized from grounded armature 192; and at armature 665 opens thelocal bridge across the talking conductors. Series relay 1|3 andslow-to-releaserelay 120 are now held energized over the previouslytraced circuit through the calling subscribers loop. At armature 61| thedeenergization of relay 610 opens a point in the original energizingcircuit v of relay 630.

When the manual operator at the main exchange answers the call, groundis connected to conductor 194, thereby completing an energizing circuit;for relay 130 as follows: from ground at the main exchange'by way ofconductor 194, normally closed springs controlled by armature 133,armature 142, and through the winding of slow-to-release relay 130 tobattery. At armature 13| relay 140 completes a point in the talkingcircuit and also substitutes the ground at the main exchange for groundthrough the winding of relay at' armature 132 maintains relay 190energized; and at armature 133 completes a locking circuit for' itselfby way of armature 142 before opening its original energizing circuit.Relay 120, upon deenergizing, at armature 12| opens a point in thecircuit of relay 140, which relay is held energized from armature 1I4 onthe series relay 1|3; at armature 123 disconnects ground from conductor194 and completes `the talking circuit; and at armature 122 disconnectsbattery extending through resistance 124 from the lower winding ofseries relay 1|3 after armature 123 has completed the talking circuit.Series relay 1I3 is maintained energized from ground at the mainexchange extending by way of conductor 194, armature 13|, through itsupper winding and from thence over the calling subscribers loop throughits lower winding, resting Contact of armature 123 and said armature,conductor 195 to battery at the main exchange. The calling subscriber isnow connected to the distant operator and may converse over the heavytalking conductors to inform the distant operator of the desiredsubscriber. The manual operator at the distant exchange completes theconnection to the desired subscriber in the wellknown manner.

It will now be assumed that the trunk conductors 194 and 195 extend toan automatic exchange and therefore the operation of relay |530completes a circuit for energizing series relay 1 i3 and the line relayof an incoming line switch in the main exchange. This circuit may betraced as follows: from ground over the short circuiting connections ofrelay 120, normally closed springs controlled by armature 13|, throughthe upper winding of series relay 1|3, and from thence over the localbridge including the resistance 631, the lower winding of relay 1|3, aspreviously described, over conductor 195 through the winding of the linerelay in the incoming line switch to battery. At armature 1|4 relay 1|3completes a circuit for energizing relay 140 and relay 140, uponenergizing, completes a circuit for energizing relay 190 and prepares acircuit for energizing relay in the same manner as previously described.The operation of relay 190 causes the trunk distributor to preselectanother idle trunk, whereupon relay 650 deenergizes as previouslydescribed. When the local bridge is opened at armature 655 by thedeenergization of relay 650 the series relay 1|3 and the line relay inthe incoming line switch at the main exchange are held energized overthe calling subscribers loop.

The operation of the line relay at the main exchange causes the lineswitch thereat to operate in the well-known manner to seize an idletrunk, at which time dial tone is transmitted back over conductors 194and 195 to the calling subscriber. In addition, ground is connected totrunk conductor 194, thereby causing the energization of relay 130 tocomplete the talking circuit. At armature 13| relay 130 completes adirect metallic loop including the calling subscribers line to enablethe local'calling subscriber to operate the automatic switches in theautomatic exchange in response to the operation of his calling deviceCD.

In response to the calling subscriber S operating his calling device CD,the automatic switches in the automatic exchange are operated in thewell-known manner to complete` the desired connection. Relay 1|3intermittently operates during the impulsing period, but since relay isslow to release the latter relay is maintained in operated position toprevent the deenergization of relay 130. Talking battery for 4both thecalling and called subscribers -is furnished from the main exchange.During conversation the following relays are in operated position in thetrunk circuit; relays 630, 660, 690, 1|3, 130, 140, 150, and 190. and inresponse to subscriber S replacing his receiver, the closed loopextending to the distant exchange is opened at the switchhook springsand series relay 1|3 thereupon deenergizes. At armature 114 relay 1|3upon deenergizing, opens the circuit of relay 140 which deenergizesafter an interval. At armature 142 relay 140 opens the circuit of relay130 which thereupon deenergizes. At armature 132 relay 130, upondeenergizing, opens the circuit of relay which likewise deenergizes andat armature 13| opens a point in the talking circuit. The automaticswitches in the main exchange are released in the well-known manner andthe trunk line is made available for other calls. In the case where thecall extended to a manual exchange the distant main-exchange operatorwould get a supervisory signal to indicate when the calling subscriberhas hung up.

Holding circuit In order to describe how local subscribers equipped witha push-button, such as pushbutton PB, can hold a trunk call while makinga local call, it will be first .assumed that subscriber S is connectedin a trunk call over the trunk line shown in Figs. 5, 6, and '7. Themainexchange subscriber is advised by subscriber S to wait on the linewhile she completes a local connection. Subscriber S now operates thepushbutton PB to ground conductors |0| and |02, thereby shuntingtheupper windings of difierential relay |4 and series relay 1|3. Thisshunt circuit extends from ground at the main exchange over conductor194, armature 13|, upper winding of series relay 1|3, normally closedsprings controlled by armature 10|, conductor 5|6, upper winding ofdifferential relay 6|4, armature 63|, conductor 56|, wiper 55|,conductor |02, through the substation circuit to ground at thepush-button PB. Series relay 1|3 is maintained energized over its lowerwinding from ground at the push-button PB by way of conductor |0|, wiper555, conductor 565, armature 63B, lower winding of differential relay6|4, conductor 691, normally closed springs controlled by armature 105,lower winding of series relay 1|3, armature 123, and over conductors 195to battery at the main exchange. Differential relay 6|4, however, isunbalanced over the circuits just traced and accordingly operates itsarmature 6|5 to energize relay 100 in its rst step by way of armature104 and its resting contact. Relay 100, upon operating in its rst step,operates only armature 103 to prepare a circuit for operating itself toits second step, and also completes the circuit for short circuiting itsupper After conversation winding. This vshort circuit extends fromground at armature 6I5, conductor 626, armature 104 and resting contact,upper winding of relay 100, armature 103, normally closed springscontrolled by armature 1|2, conductor 621, armature 69|, and through theresting contact of armature 643 to ground.

When subscriber S releases the push-button PB ground is removed from theconductors and |02, thereby again completing the energizing circuitthrough the upper and lower windings of differential relay 6|4 to causesuch relay to deenergize. At armature SI5 diiferential relay 6|4, upondeenergizing, removes the short circuit from around relay 100, therebycausing relay 100 to operate to its second step. This circuit may betraced as follows: from ground at armature 643 and resting contact,armature 68|, conductor 621, normally closed springs controlled byarmature 1 I2, armature 103, and through the upper and lower windings ofrelay 100 to battery.

The remaining armatures (indicated by the Roman numerals II) nowoperate. At armatures 10| and 105 two-step relay 100 completes a holdingbridge including resistance 106 across the talking conductors extendingto the main exchange; at armature 102 completes an obvious circuit forenergizing relay 680; and at armature 104 prepares a circuit forenergizing slow-to-release relay`1|0. Relay 680, upon energizing, atarmatures 68| and 685 connects the windings of line relay 6I0 in bridgeof the line extending to subscriber S. Atrarmature 682 relay 680connects conductor |24 to relay 620; at armature 683 opens a point inthe circuit of relay 680, which, however, at this time is maintainedenergized in response to the operation of relay 6|0; and at armature 664grounds conductor |22.

Line relay 6| 0 is now energized over the following circuit: from groundthrough the lower winding of relay 6I0, armature 605, armature 685,lower winding of differential relay 6|4, and thence over the callingloop to the line of substations S and back to the upper winding ofdifferential relay 6|4 and from thence by Way of armature 68| andarmature 60| through the upper winding of relay 6|0 to battery. Atarmature GII relay 6|!) connects marking battery through the winding ofcut-off relay 600 to conductor |23 and the corresponding bank contactsin the local iinders; at armature 6|2 completes a circuit formaintaining slow-to-release relay 690 in energized position; and atarmature 6|3 grounds the local nder start conductor 9 to operate thestart relay 420 to cause a nder of an idle local nder connector link tohunt for and find the marking potential connected to conductor |23.

Start relay 420 in the nder connector distributor is energized in thesame manner as .previously described and at armature 42| operates relay400. At armature 402 relay 400 operates relay 4|0, completes the ndertest circuit at armature 40| and completes the circuit to the findermagnet |68 at armature 403.v

The finder magnet |68 and line stepping relay 230 operate as previouslydescribed to step the wipers of the inder until the marking potential onconductor |23 is found by test wiper |53. When test wiper |53 engagesits twentyfirst bank contact, relay 600 energizes in series with relays220 and 230 as follows: from ground through the llower winding of relay230, normally closed springs controlled by armature 226, lower windingof relay 220, conductor 228, wiper 4|2,

armature 40|, wiper 4I3, conductor |63, wiper |53, conductor |23,armature 6|I, and through the windingof cut-oil relay 600 to battery. Atarmature 22| relay 220 again completes the circuit for energizing relay2|0; at armature 222 completes the circuit for energizing relay 280; atarmature 223 prepares the circuit for the 'series relay 210; at armature224 grounds the guard conductor 221 to cause the finder connectordistributor to preselect another idle link; at armature 225 groundsconductor |23 by way of conductor |63 and wiper |53 for maintainingrelay 600 energized; and at armature 226 disconnects the lower windingof relay 220 and connects the lower talking conductor to line relay 230.At armature 2|| relay 2|0 completes a circuit including both talkingconductors for line relay 230, which is maintained energized; atarmature 2|2 maintains relay 220 energized; at armature 2|3 prepares apoint in the connector test circuit; and at armature 2|4 prepares apoint in the impulsing circuit.

Line relay 230 is now energized over both windings in series over thecalling loop as follows: from ground through the lower winding of relay230; working contact and armature 226, armature 206, conductor |65,wiper |55, conductor |25, armature 68|, through the upper winding ofdiierential relay 6|4, armature 63|, conductor 56|, wiper 55|, conductor|02, through the substation loop to conductor IOI, wiper 555, conductor565, armature 636, through the lower winding of differential relay 6|4,armature 685, conductor |2I, wiper I5I, conductor |6I, armatures and 2|I, and through the upper winding of line relay 230 to battery. Atarmature. 28| relay 280 prepares a point in the circuit used intransferring a call, and at armature 282 prepares a point in the circuitthrough the upper winding of local release relay 200 to automaticallycause the release of the local nder connector link in case the connectoris operated to originate or answer a trunk call. At armature 283 relay280 opens a point in the locking circuit of switching relay 290 to makeit release, when operated later, dependent upon the operated conditionof the local release relay 200.

In the trunk circuit cut-off relay 600, upon energizing, at armatures60| and 605 disconnects relay 6|0 from the talking conductors |25 and|2I. At armature 602 relay 600 completes its own locking circuit togrounded conductor |23; at armature 603 connects the grounded conductor|23 through the winding of relay 690 to maintain the latter relayenergized; and at armature 604 disconnects ground from finder startconductor 9. Relay .6|0, upon deenergizing, at armature 6|| opens apoint in the original energizing circuit of relay 600; at armature 6|2opens a point in the original energizing circuit of relay 690; and atarmature 6|3 opens a further point in the circuit to the finder startconductor 3.

The line of subscriber S is now connected to the local finder connectorlink shown in Fig. 2 and in response to the operation of the callingdevice CD in accordance with the telephone number of the desired localsubscriber the line relay 230 is correspondingly operated over thecircuit just traced. In the same manner as previously described, theconnector is operated to complete the connection to the desired localsubscriber.

In case subscriber S at this time should attempt to answer another trunkcall or originate a trunk call while holding a trunk, then local releaserelay 200 is operated to automatically release the local nder connectorlink to prevent such trunk call. If subscriber S attempts to answeranother trunk call, local release relay 200 is energized from themarking ground at armature 323 as follows: from ground by way ofarmature 323, when marginal relay 3|5 is energized as previouslydescribed, conductor 330, eighth bank contact and wiper 352, conductor233, armature 282, armature 21|, and through the upper winding of localrelease relay 200 to battery. In case subscriber S attempts to originatea trunk call, local release relay 200 energizes from marking ground atarmature 361 and marking relay 362 is energized as previously described.This circuit may be traced from ground at armature 361, conductor 313,ninth bank contact and wiper 352, conductor 233, armatures 282 and 21|,and through the upper winding of local release relay 200 to battery. Theoperation of local release relay 200 at' armatures 20| and 206 opens thecircuit ofline relay' 230 to cause its deenergization and at armature202 opens the locking circuit of switching relay 290 to cause the latterrelay to deenergize. The local nder connector link in this case isreleased in the same manner as previously described.

Assuming now that subscriber S has completed a call to another localsubscriber and that subscriber S now wishes to release the localconnection and return to the held trunk, in order to return to the heldtrunk subscriber S pushes the push-button PB, thereby unbalancing thedifferential relay Y6||l to cause its energization. Differential relay6|4, upon energizing, at armaturev 6|5 completes the circuit by way ofconductor 626 and armature 104 and its working contact for energizingslow-to-release relay 1|0. At armature 1|I relay '|I0 temporarily placesa bridge including resistance 6|'I across the talking conductors 56| and565 to reduce the click in the receiver of the substation set. Atarmature 1|2 relay 1|0 completes a new circuit for holding two-steprelay in energized position from grounded conductor 626. When thepush-button PB at substation S is released, diierential relay 6I4deenergizes and at armature 6|5 disconnects ground from conductor 626,thereby opening the circuit of the two-step relay 100 and slow-toreleaserelay 1|0. At armatures 10| and 105 two-step relay 100 disconnects thetrunk-holding bridge including resistance 106 from across the trunkconductors 194 and 195 and completes the talking circuit to the line ofsubstation S. At armature 102 relay 100 opens the circuit of relay 680,which thereupon deenergizes; at armature 103 opens a point in its owncircuit; at armature 104 opens a further point in the circuit of relay100; and at its resting contact prepares its original energizingcircuit. At armatures 60| and 685 relay 680 opens the circuit to linerelay 230 in the local nder connector link to cause the deenergizationof this relay and the release of the local finder connector link aspreviously described. At armatures 683 relay 680 opens one point in thecircuit of relay 690 at its working contact but at its resting contactcompletes another circuit from grounded armature 663 for maintainingthis relay in operated position. At armature 684 relay 680 disconnectsground from conductor |22 to cause the deenergization of relay 280 inthe local finder connector link. Slow-to-release relay 'H0 deenergizesafter an interval and at armature 1| opens the bridge across conductors56| and 565 to permit conversation thereover. At armature 1|2 relay 1|0prepares a point in the circuit for operating twostep relay '|00 in itssecond step. The subscriber S and the distant main-exchange subscriberare again connected over the previously traced talking circuit' andafter conversation may release the connection in a manner similar tothat previously described.

'Irunk lines in use in calls originated by the local subscriber are heldwhile the local subscriber completes a local connection and returned toin the same manner as described for the trunk line in use on incomingcalls.

Transfer circuits In order to describe how local subscribers maytransfer trunk lines from one local line to another,'it vwill be assumedthat subscriber S is connected to the trunk line shown in Figs. 6 and 7and that subscriber S desires to transfer the call to subscriber S. Inthe samemanner as previously described subscriber S operates herpush-button PB to cause the two-step relay 1'0'0 in the trunk to closethe trunk holding bridge and to cause a finder of an idle local finderconnector link to be connected to conductors |'2l to |25, inclusive, ofthis trunk line. After receipt of dial tone subscriber S dials thelnumber of subscriber S to ca use the connector to complete-',theconnection to the line of subscriber S' as previously described. Thetalking circuit between subscriber S and subscriber S extends throughythe local -iinder connector link and trunk circuit as' follows: fromlline conductors [0| and |02 of line S, wipers 55| and 555 of the trunkilnder, conductors l56| and 565. armatures 55| andf6'36, through theupper and lower windings of differentialrelay 6|4 in parallel, armatures68| and 635, conductors |25 and |2I, wipers |55 and |'5|, conductors |6|and |65, armatures 20|' and 206, armatures 2 and 226, through the upperand lower talking condensers and the upper' and lower windings ofdiierential relay 244, arg maturesy 26| and 263, armatures 25| and 225;wipers 35|- and 355. and thence over the line conductors 30| and-302 tosubstation S'.

Subscriber S now informs subscriber 8' that such subscriber is desiredon a trunk connection. Subscriber S' thereupon operates his push-buttonPB to ground conductors 30| and '252 through the substation circuit.Relay 244 in the local nder connector link is a diilerential relay andhas both its windings connected in series over the called substationloop as follows: from grounded conductor 264, armature 262, lowerwinding. of combined busy and back-bridge relay 250, lower winding ofdiiferential relay 244,

working contact and armature v263, armature 236, conductor 239, wipers356, conductor 352, and thence through the substation ircuit toconductor 30|, wiper 35|, conductor 2 2, armature 29|, armature 26| andworking contact, upper winding of differential relay 244, and throughthe upper winding of relay '250 to battery. Since both windings of thedifferential relay are equal and oppose each other, the differentialrelay 244 does vnot therefore operate.

Now, when the push-button PB at substation S' is operated to groundconductors 30| and 302, the lower winding of differential relay 244 isshunted, thereby causing the differential' relay 244 to. operate itsarmature 245. At armature 245 differential relay 244 completes a circuitfor operating the two-step relay 240 in its first step as follows: fromground at armature 604, conductor |22, wiper |54, conductor |64, amature

